The decision to cull it would be based on your situation. Is this chicken a pet? Do you feel you are at a place in your life where you can care for a blind chicken?
If I had a blind chicken my first year of raising them I may have been willing to invest the time. Now, with more responsibilities in my life I know I would not be able to responsibly care for it and it would suffer.
You need to decide if you can care for it's special needs for the long haul. If your situation changed after a year of bonding to it, would you have the heart to cull it then?
My friend is raising chicks for the first time. She just discovered that one of her three week olds is blind in one eye. She and her children want to try and raise it, but with 18 hens all together, I fear for it's well being.
I understand the emotions of this difficult situation. You have to define where you stand in the area between pet and livestock.